As used herein, the term vitreous type coating means a coating that has the appearance of glass or enamel, which can be either organo-mineral or entirely mineral.
As used herein, the term organo-mineral vitreous coating means a coating made up of a material of the sol-gel type (i.e. obtained through the sol-gel route) whose lattice is essentially inorganic, but which includes organic groups, due in particular to the precursors used and the firing temperature of the coating.
As used herein, the term entirely mineral coating means a coating made up entirely of an inorganic material, free of any organic groups. Such a coating can also be obtained by the sol-gel route with a firing temperature of at least 400° C., or from precursors of the tetraethoxysilane (TEOS) type with a firing temperature that can be less than 400° C.
In the field of vitreous type non-stick coatings intended for cookware, sol-gel coatings are known, and in particular those obtained from metal alkoxides based on silica (silanes) or based on alumina (aluminates).
These coatings are now highly developed in the cookware field, because they make it possible to obtain colored coatings with especially good resistance to scratching and heat.
Such coatings, however, have limited adhesion to metal substrates, particularly to aluminium, stainless steel and cast iron substrates.
To overcome these problems, the person skilled in the art know to prepare the substrate's surface by chemical treatment (of the chemical etching type, for example) or mechanical treatment (by brushing or sandblasting, for example), or even a combination of these treatments.
Even when such treatments are implemented, however, the adhesion to the substrate of the non-stick coating remains limited, in particular when the non-stick coating is subjected to a mechanical deformation such as a shock or a perforation, for example to set a rivet or a mounting stud.
Thus, when cookware whose bottom has an inner face coated with a sol-gel type non-stick coating is subjected to powerful shocks, marring under impact is observed which is accompanied by radially propagating cracks, even if the bottom's inner face has been previously sandblasted or brushed.
It follows that considerable precautions must be taken during manufacture of such cookware, which is manifested by high reject rates and low production speeds.